Wheel slip can occur as a result of engine drag or braking on the driven wheels of a vehicle. More particularly, when a driver suddenly releases the throttle, the engine drag force can become larger than the frictional force between the road and the driven wheels. As a result, the driven wheels slip or skid on the road surface. Vehicle stability can be reduced, especially in the case of a rear-wheel drive vehicle traveling on a low-coefficient of friction surface, such as wet pavement, gravel, ice or snow covered roads and the like.
Vehicle stability systems sometimes include an engine drag control (EDC) module that reduces wheel slip during closed throttle, non-braking deceleration. In general, the EDC module generates a drag torque request that indicates an increase in engine torque that is required to reduce wheel slip and improve vehicle stability. The EDC module can be implemented by an anti-lock braking system (ABS) module and an engine control module (ECM) or other modules and controllers. The ABS module determines the drag torque request and transmits it to the ECM module. The module ECM regulates the engine based on the drag torque request. The drag torque request and resultant throttle control is generated by the EDC module and is not operator generated. Therefore, the drag torque request should be secure and the resultant throttle control not startling to the operator. In other words, the drag torque request should not produce an unsafe driving condition or produce a sudden, high engine torque output that is startling to the operator.